Small, sleek but a bit heavier

The small “S” on the back and the pink colour are the iPhone 6S’s only differentiating marks compared to last year’s iPhone. Photograph: Samuel Gibbs for the Guardian

The iPhone 6S is the spitting image of last year’s iPhone 6. Side-to-side, back-to-back the only visible difference is a small “S” printed on the back and an extra 0.2mm in thickness. A pink version is also available, of course, if you want everyone to know you have the very latest smartphone.

It feels reassuringly solid and smooth in the hand compared to the iPhone 6, and it is slightly less slippery. It’s right on the limit of what I can use with one hand and still reach the top of the screen, which you need to be able to do within iOS.

The iPhone 6S’s screen, with 326 pixels per inch, has a relatively low pixel density compared to most other flagship smartphones. The denser the pixels, the crisper the screen appears. Lower density is particularly noticeable around text and the edges of icons.

The iPhone 6S’s 4.7in screen is noticeably less sharp than the 5.5in 401ppi screen of the iPhone 6S Plus, or the 577ppi 5.1in screen of the Samsung Galaxy S6.

While it is similar to the Sony Xperia Z5 Compact’s 323ppi screen and you may not notice the reduced clarity unless you put it side by side with a phone like the Galaxy S6, it really is time Apple increased the pixel density of its smaller flagship phone to at least match that of its phablet.

As fast as an iPhone can be

The speaker in the bottom of the iPhone is one of the best sounding smartphone speakers available, but is easily blocked by a hand. Photograph: Samuel Gibbs for the Guardian

The iPhone 6S has the same dual-core A9 processor and 2GB of RAM as the 6S Plus and performs similarly.

It’s as snappy as an Apple smartphone can currently be, limited by the fixed duration of iOS 9’s animations, all of which are as smooth as they were on the iPhone 6. It’s not nearly as snappy as Samsung’s Galaxy S6, which is not held back by the same animation speed limit.

A couple of larger apps and heavier processes, such as video or photo editing, are slightly faster to load and get work done than last year’s iPhone. Switching between apps is also slightly faster and the Siri suggest screen on the left-most homescreen within iOS 9 also loads faster on the iPhone 6S compared to the iPhone 6.

Apple claims the A9 is 70% faster than last year’s A8 but not many apps are available yet to take advantage of the extra speed.

I found the iPhone 6S became warmer than the iPhone 6S Plus, particularly when downloading or accessing content via the mobile broadband connection rather than Wi-Fi.

Call quality was excellent and reliable, with no dropped calls in my testing on EE’s mobile network in London. Wi-Fi calling was also excellent and only took around a second to log on when connecting to Wi-Fi.

Has anyone got an iPhone charger?

Battery life is poor for a top-end smartphone, meaning there will be no abatement of the periodic shouts of ‘has anyone got an iPhone charger’ across the office. Photograph: Samuel Gibbs for the Guardian

Battery life is the iPhone 6S’s biggest problem. During the week the phone failed to make it past 11pm after leaving the charger at 7.30am in the morning.

I used the iPhone as my primary device, receiving hundreds of emails and push notifications, conducting 2.5 hours of browsing, three hours of music playback via Bluetooth headphones, taking a couple of pictures and playing the odd game of Angry Birds 2 on the train home.

At the weekend it spent most of the day sitting on a table untouched, but I still went to bed with only 30% charge left. Apple’s new Low Power Mode made little appreciable difference in real-world use.

Apple has chosen weight and thickness over battery life, which is a poor choice. Your experience may vary, but I suspect you will have to charge the iPhone 6S twice a day.

iOS 9

The app switcher in iOS 9 is fast and fluid on the iPhone 6S. Photograph: Samuel Gibbs for the Guardian

The iPhone 6S comes with iOS 9 pre-installed; the same software that runs on any iPhone from the 4S and newer. There are a few features such as Live Photos and always-listening Siri which are exclusive to this year’s iPhones.

iOS 9 seems better designed for the smaller phone. For example, menu options to go back are placed in the top left hand corner, which I can reach with only one hand. The tightly kerned typeface San Francisco is also designed to fit more text on a smaller screen.

3D Touch

3D Touch senses pressure on the screen to invoke gesture-based actions, such as pop-up menus. Photograph: Samuel Gibbs for the Guardian

The new pressure-sensitive screen provides options for more gestures based on pressing harder. Generally this invokes a pop-up menu similar to a right click. Homescreen icons will show a quick action menu, while Instagram shows recent photos from users when pressing harder on their username.

The “peek” and “pop” gestures, as Apple calls them, allow users to preview an email, for example, without opening it by pushing harder. Releasing and pushing harder again opens it fully. It’s useful in the Calendar app to preview a day in month view, but 3D Touch lacks any killer features for now.

Touch ID

The Touch ID fingerprint sensor under the home button is much quicker than Apple’s previous efforts, unlocking in under a second and recognising my thumb 99% of the time.

It makes using Apple Pay a lot faster and less clumsy, although some have complained that you can’t see notifications on the lockscreen because it unlocks too fast. That’s what an Apple Watch is for, I suppose, or you could use another finger.

Taptic Engine

The Taptic Engine creates much sharper, more defined vibrations. It feels great in the hand, but I found it too weak in the pocket without switching to a much more aggressive vibration pattern in the Settings app.

Camera

The 12-megapixel camera brings the iPhone up to scratch with the latest smartphone cameras from its rivals. Photograph: Samuel Gibbs for the Guardian

The iPhone 6S’s new 12-megapixel camera is one of the best available on a smartphone, but it is not leagues ahead of the competition anymore and only slightly improved over the iPhone 6.

Photos are captured with good detail and excellent colour balance. Low light performance is good too, as is video recording, which is smooth when captured at 60 frames per second.

The lack of optical image stabilisation when compared to the 6S Plus was not particularly noticeable for normal shots, but video and photos shot in low light were slightly more shaky and blurred, particularly towards the end of a night out.

Recording 4K video takes up 300MB of storage space per minute, producing decent if not exceptional video, while the 3MB Live Photos are an interesting novelty of which I easily became bored. I ended up shooting more videos after becoming frustrated with the poor quality and low frame rate of Live Photos.

Price

The iPhone 6S costs £539 for 16GB of storage, £619 for 64GB and £699 for 128GB in silver, dark grey, gold and pink.

Avoid the 16GB if you have the budget. Photograph: Samuel Gibbs for the Guardian

Verdict

The iPhone 6S has the potential to be the best smaller smartphone on the market, but its short battery life is deeply frustrating.

Apple’s iOS 9 fits and works better on the 4.7in screen than on the larger iPhone 6S Plus, the bezels and size of the device compared to the screen are more suited to the smaller size and it feels great in the hand.

But it can’t get you home on a night out, it can’t pull double duty as a camera on holiday and it can’t be a commuter’s boredom destroyer without a top up during the day.